Setting check mark for SelectManyCheckbox item

Question

I'm trying to set the check mark for a SelectManyCheckbox item from a backing bean and cannot find any explicit explanation or example to do this. This would be used to have a command button select all checkboxes and a command button to clear all checkboxes.
I've been trying to set the SelectItem value, but while log messages suggest what is desired has occurred, nothing visually changes. Here's the key parts of what I'm working with so far.
<h:selectManyCheckbox
  id="patients" layout="pageDirection"
  value="#{SelectBean.patientsSelected}" >
  <f:selectItems value="#{SelectBean.patientSelects}" />
</h:selectManyCheckbox>
<h:commandButton type="submit" value="Select All Patients"
  id="allPatients"
  action="update"
  actionListener="#{SelectBean.onSelectAll}" />
private Collection<SelectItem> patientSelects;
private List<String> patientsSelected;
for (int i = 0; i < 10; i++) {
  value = false;
  label = locationSelected + "-" + "patient" + Integer.toString(i);
  patientSelects.add(new SelectItem(value, label));
public void onSelectAll(ActionEvent event) {
  for (Iterator it = patientSelects.iterator(); it.hasNext();) {
    SelectItem si = (SelectItem) it.next();
      si.setValue(true);
}

Answer 1

the arrayList you suggest doesn't even contain these items.You have to prefill the patientsSelected yourself to mark preselected items.
Basic example:<h:selectManyCheckbox value="#{myBean.selectedItems}" />
    <f:selectItems value="#{myBean.selectItems}" />
</h:selectManyCheckbox>MyBeanprivate List<String> selectedItems; // + getter + setter
private List<SelectItem> selectItems; // + getter + setter
    // Prefill selectItems.
    selectItems = new ArrayList<SelectItem>();
    selectItems.add(new SelectItem("value1", "label1"));
    selectItems.add(new SelectItem("value2", "label2"));
    selectItems.add(new SelectItem("value3", "label3"));
    selectItems.add(new SelectItem("value4", "label4"));
    selectItems.add(new SelectItem("value5", "label5"));
    // Preselect item #2 and #4.
    selectedItems = new ArrayList<String>();
    selectedItems.add("value2");
    selectedItems.add("value4");
}